The shell-and-tube heat exchanger-type reactor may be used for catalytic vapor phase oxidation, for example, for a process of manufacturing unsaturated acid from olefin using a catalyst in vapor.
Generally, the shell-and-tube heat exchanger-type reactor includes reaction tubes filled with at least one kind of granule catalyst, which receives reaction gas provided through a pipe. In the heat exchanger-type reactor, the reaction gas contacts with and reacts upon the catalyst in the reaction tubes so as to generate a desired product. Reaction heat generated in the reaction is transferred to and removed by heat transferring media which circulate in shells provided on a peripheral surface of the reaction tubes and are maintained at a predetermined temperature. The reaction mixture containing the desired product is carried through a pipe to a recovery and refining device.
Generally, catalytic vapor phase oxidation is a highly exothermic reaction. Therefore, it is important to control reaction temperature in a certain range as well as to reduce the size of the temperature peak at a hot spot occurring in a reaction zone. Specifically, it is very important to rapidly detect a location of the heat point in the catalyst layer and to accurately measure the size of the temperature peak at the hot spot, in consideration of process conditions, feed composition, and structure of catalyst layers.
In order to measure temperature of the hot spot, the conventional shell-and-tube heat exchanger-type reactor includes a plurality of reaction tubes each of which has a thermo-well tube mounted therein and at least one thermocouple. Some of the thermocouples are fixed type thermocouples which are located at fixed points in the reaction tube, while the rest are movable type thermocouples which can be inserted into and drawn into and out the thermo-well tube as well as moved within some range of the thermo-well tube.
In such a temperature measuring device, the role of the movable thermocouple is very important. As described above, the location of the hot spot is determined according to the process conditions, the feed composition, and the structure of the catalyst layers, while the size of the temperature peak at a hot spot is also determined according to the heat controlling capacity of the heat transferring media. Therefore, it is necessary to insert or draw the movable thermocouple into and out the thermo-well tube so as to monitor the accurate location and size of the hot spot.
Further, the movable thermocouple helps an operator to obtain the temperature profile of the entire catalyst bed for the whole length of the reaction tube. There are much information obtained from the temperature profile of the catalyst bed, through which the operator can easily and visually analyze whether the hot spot is occurred, whether the catalyst particles are evenly distributed, whether it is necessary to control the reaction temperature, and whether the reactor normally operates.
However, since the temperature of the catalyst layer in the reactor having the fixed catalyst layer generally increases to 200° C.˜500° C. due to the highly exothermic reaction, the thermo-well tube protecting the thermocouple is thermally expanded and extremely deformed due to bending or twisting, thereby making it difficult to move the thermocouple.
In order to obtain the temperature profile of the catalyst layer, the thermocouple having a low mechanical strength should be inserted into the reaction tube along its whole length, i.e. from several meters to several tens of meters in the thermo-well tube. However, the thermocouple is subjected to a great friction resistance while moving in the thermo-well tube deformed by the thermal effect, so that its sensor may fail to reach a desired point in the thermo-well tube. Furthermore, the thermocouple may be broken due to an unsuitable insertion thereof.
When the thermocouple is broken while it is being inserted in the thermo-well tube, there is no way to withdraw the inserted broken thermocouple from the thermo-well tube, resulting in a seriously negative effect on the monitoring of the temperature.